Field of the Invention
The present invention relates to an image pickup apparatus which performs focus detection by a phase difference detection method.
Description of the Related Art
Conventional image pickup apparatuses which perform focus detection of a phase difference detection method (imaging-plane phase difference method) by using focus detection signals from an image pickup element are known.
U.S. Pat. No. 4,410,804 discloses an image pickup apparatus using a two-dimensional image pickup element in which a single microlens and a plurality of divided photoelectric conversion portions are formed for each pixel. The divided photoelectric conversion portions receive light beams passing through different partial pupil regions of an exit pupil of an imaging lens via the single microlens for dividing the pupil. An image shift amount can be calculated based on each of focus detection signals that are received by the divided photoelectric conversion portions (focus detection pixels) to perform focus detection by a phase difference detection method. Japanese Patent Laid-open No. 2001-083407 discloses an image pickup apparatus which combines respective focus detection signals received by the divided photoelectric conversion portions.
Japanese Patent Laid-open No. 2000-156823 discloses an image pickup apparatus which includes a pair of focus detection pixels arranged partially in a part of an array of a plurality of imaging pixels. The pair of focus detection pixels receive light beams passing through different regions from each other in an exit pupil of an imaging lens for dividing the pupil. An image shift amount can be calculated based on focus detection signals of the pair of focus detection pixels to perform focus detection by the phase difference detection method. According to the focus detection by the phase difference detection method (imaging-plane phase difference method), a defocus direction and a defocus amount can be simultaneously detected by the focus detection pixels of the image pickup element, and accordingly it is possible to perform high-speed focus control.
However, in the imaging-plane phase difference method, a spatial frequency band of a focus detection signal for the focus detection may be different from a spatial frequency band of an imaging signal for generating a captured image. In this case, a difference between a detected in-focus position based on the focus detection signal and a best in-focus position based on the imaging signal occurs, and accordingly it is difficult to perform the focus detection with high accuracy.